KS 150
From Wikipedia, the free encyclopedia
KS 150 (also known as A-1) is a heavy water gas cooled reactor (HWGCR) nuclear reactor. Single unit was used in the power plant A-1 in Jaslovské Bohunice, Czechoslovakia. The power plant suffered a series of accidents, the worst being the accident from February 22, 1977 rated INES-4. In 1979 the plant was decomissioned.
Contents |
[edit] History
Decision to build a nuclear power plant in Czechoslovakia was made in 1956. The construction of the plant (A-1) in Jaslovské Bohunice (western Slovakia) started in 1958 and unexpectedly took 16 years. A-1 was opened on October 24, 1972.
The KS 150 reactor was designed in the Soviet Union and completely built in Czechoslovakia by Škoda Works. This type of reactor was never deployed before. One advantage of the design was to be able to use the uneriched uranium mined in Czechoslovakia, similarly to the CANDU reactor.
Because of its experimental design the power plant suffered from accidents resulting in over 30 unplanned shutdowns. On January 5, 1976 two workers were killed due to leak of carbon dioxide used as a coolant. The most serious accident from 1977 was rated INES-4. The damage could have been repaired with a large investment but on May 17, 1979 the government, dissatisfied with the costs, low performance and accidents, decided to decomission the plant. Plan to build the second reactor block A-2 was cancelled.
The accidents were kept in secret although wild stories had circulated among the public.
The decomissioning, decontamination and dismanting the plant still continues, see 1997 report for the schedule.
[edit] Technical details
KS 150 is a heavy water moderated, gas cooled reactor (HWGCR) able to refuel during operation.
[edit] Active zone
Translated from [1]: Metal uranium in form of a thin string is covered by compound of magnesium and beryllium. Around 70 strings form a fuel rod. The reactor wessel is a cylinder made from an aluminium compound filled by heavy water used as a moderator. The fuel channels are vertical, each containing single fuel rod coolex by flow of carbon dioxide. The active zone is placed in a pressurized wessel which allows refuelling during operation. The heavy water is cooled in a separate circuit.
The gas used as a primary coolant is forced to flow around the fuel rods, is heated by them and then piped to six steam generators. The water steam powers three turbines with electricity generators.
[edit] Parameters
- Fuel: unenriched metal uranium, 23.1 tons in the reactor.
- Active zone: diameter 3.56 m, height 4 m.
- The coolant gas on the output from reactor: pressure 5.4 MPa, temperatire 426°C.
- Conversion efficiency: 18.5%.
- Moderating heavy water: temperatire 65°C
- Capacity: 143 MWe.
[edit] 1977 accident
On February 22, 1977, during fuel change, a combination of human mistake and design problem caused the worst nuclear accidetnt in Czechoslovakia. Part of fuel rods was replaced while the reactor was active. Humidity absorber covering the rods was not removed causing local overheating of the fuel (trasmission of heat to the coolant gas was reduced). The active zone was damaged, heavy water got in contact with the coolant and both primary and secondary circuits were contaminated.
The accident was rated as level 4 on International Nuclear Event Scale (for comparison, the Three Mile Island accident was rated level 5).
[edit] External links
- Short description, schema (in Czech)
- Decommissioning of the reactor (detailed report, PDF)
